can one have 2 different Operating Systems installed and running on 2 different HDDs (In my case it is win2k serer and fedora core 3) . If possible how would my grub loader look like ?

Easiest would be just clean install 2k server and Fedora afterwards - the FC installer should do the right thing.

We could give more detailed help if you told use exactly what you have and what you want to do.

Ok here is my problem.
I have a system with 2 HDDs (300 GB) and i want to configure my boot loader with linux from second hard disk along with linux and windows on my first hard disk.

Do you have any operating systems installed at the moment?

If nothing or only Windows at the moment then just install Windows (if needed), one of the Linuxes (don't install a bootloader or put it in the Linux partition) and the other Linux putting GRUB in the MBR.

Or. Install Windows (if needed), Linuxes with bootloaders in partitions and configure the windows bootloader as needed (see the sticky thread on dual booting).

I have installed all of them (actually not me). so the system now has all the 3 os and my grub has linux and windows of the first HDD, and i want to add Linux of the second HDD to add to it.

It's perfectly possible to install Linux on your second harddisk.

If you let the installation process overwrite your Master Boot Record with a new GRUB install, then it will automatically create its boot loader configuration file for you, and you will be able to choose between your Windows and your Linux system as soon as you reboot from your harddisk.

If you already have a working GRUB installed to your Master Boot Record, you may prefer to do a new GRUB install onto your new Linux boot partition instead; the configuration file will be set up for you, but it will not get loaded when you reboot your system. You can, however, manually switch to the newly installed GRUB copy; just type a "c" (for "command line"), without the quotes, of course, on the GRUB screen, and tell it to chainload your newly installed system - something like this:

root (hd1,x)
chainloader (hd1,x)
boot

(where "hd1" refers to your second harddisk, and "x" will have to be replaced with the number of the partition on which you installed the new GRUB copy - 0 is the first partition, 1 is the second partition, etc.).

That will bring you to the new GRUB copy, from which you can start up your newly installed Linux system. Once you're there, you can open up the new GRUB configuration file, look for the entry that describes the new Linux system, and copy that entry over to your "main" GRUB configuration file (i.e., the one that gets used by the GRUB copy that you installed onto your Master Boot Record).

This is actually the easiest way to learn about the contents of the GRUB file.